The invention relates to a rotary piston machine of the type having a housing, a prismatic cavity in the housing, the cross section of this cavity being an oval, and a rotary piston movable in this cavity, the cross section of this rotary piston being also an oval, the order of the rotary piston oval being different from the order of the oval forming the cross section of the cavity. The rotary piston, in operation, moves, in consecutive intervals of motion, from one blocking position to the next. In each such blocking position, the axis about which the rotary piston rotates, changes from one position to another one. Thus the rotary piston, alternatingly, rotates about different axes of rotation. During this rotary movement, two working chambers are defined between the inner wall of the cavity and the rotary piston, the volume of one working chamber increasing, while the volume of the respective other working chamber decreases. The rotary piston has an axial aperture therethrough with an internal gear, which meshes with gear means for driving the rotary piston machine or for being driven thereby.
In mathematics, an “oval” is a non-analytical, closed, convex figure which is composed of circular arcs. The circular arcs join each other continuously and differentially. In the points in which the circular arcs join, the curve is continuous. Also the tangents of the two joining circular arcs coincide there. The curve is differentiable. In the points, where the circular arcs of different radii of curvature join, the second derivative, which determines the curvature, makes a saltus. The oval consists, alternatingly, of circular arcs having a first, smaller radius of curvature and a second, larger radius of curvature. The order of the oval is determined by the number of pairs of circular arcs having the first and second radii of curvature. An oval of second order or bi-oval is “ellipse-like” with two diametrically opposite circular arcs of smaller diameter and two circular arcs of larger diameter.
Rotary piston machines of this type are known.
U.S. Pat. Nos. 3,967,594 and 3,996,901 disclose rotary piston machines having an oval rotary piston in an oval cavity. The cross section of the rotary piston is bi-oval. This bi-oval rotary piston is movable in a tri-oval chamber. In this prior art rotary piston machine, complex transmissions are provided to transmit the rotary movement of the rotary piston to an output shaft.
DE 199 20 289 C1 describes a rotary piston machine, wherein the cross section of a prismatic cavity defined in a housing is tri-oval with three pairs of continuously and differentially joining first and second circular arcs of alternatingly a smaller radius of curvature and a larger radius of curvature. A rotary piston having bi-oval cross section is guided in this cavity. The bi-oval cross section of the rotary piston is formed of alternatingly first and second circular arcs with the smaller and larger, respectively, radii of curvature of the tri-oval cross section of the cavity, these circular arcs, again, joining continuously and differentially. The bi-oval rotary piston, in the cavity, carries out the intervals of motion with “jumping” instantaneous axes of rotation described above. The rotary movement of the rotary piston is picked-off in a very simple way: A shaft extends centrally through the tri-oval cavity, i.e. along the line of intersection of the planes of symmetry of the cavity. The shaft carries a pinion. The rotary piston has an oval aperture with an internal gear. The long axis of the cross section of the aperture extends along the short axis of the bi-oval cross section of the rotary piston. The pinion continuously meshes with the internal gear.
In the prior art rotary piston machine, a housing defines a prismatic cavity, the cross section of which is such an oval of odd order, thus, for example, an oval of third order. The cavity has cylindrical inner wall sections with, alternatingly, the first, smaller and the second, larger radii of curvature. In such an oval of third (fifth or seventh or higher) order, rotary piston is rotatable, the cross section of which is an oval, the order of this rotary piston oval being by one smaller than the order of the oval of the cavity. Even though the oval used for the rotary piston has a higher order, it has a twofold symmetry, i.e. it is mirror-symmetrical with respect to two mutually orthogonal axes. This rotary piston has two diametrically opposite cylindrical surface sections, the radius of curvature of which is equal to the smaller (first) radius of curvature of the oval of the cavity. If the cross section of the rotary piston is an oval, the second, larger radius of curvature of this oval is equal to the second, larger radius of curvature of the oval defining the cavity. In a certain interval of motion, a first of these cylindrical surface sections of the rotary piston engages a cylindrical inner wall section complementary thereto of the cavity, which inner wall section has the same radius of curvature. The second, diametrically opposite cylindrical surface section of the rotary piston slides along the opposite, larger radius of curvature cylindrical inner wall section of the cavity. In this way, two working chambers are defined by the rotary piston, of which, during the rotation of the rotary piston, one increases in volume and one becomes smaller. In this interval of motion, the rotary piston rotates about an instantaneous axis of rotation. This instantaneous axis of rotation coincides with the cylinder axis of the first cylindrical surface section. This instantaneous axis of rotation has a well-defined position relative to the rotary piston. In this interval of motion, the instantaneous axis of rotation coincides, of course, also the housing-fixed cylinder axis of the smaller radius of curvature inner wall section, in which the rotary piston rotates. This rotation continues, until the second cylindrical surface section of the rotary piston reaches a blocking position. In the blocking position, the second cylindrical surface section engages the smaller diameter inner wall section joining the opposite inner wall section of larger diameter.
A further rotation of the rotary piston about the hitherto existing instantaneous axis of rotation is not possible. Therefore, the instantaneous axis of rotation, for the next interval of motion, “jumps” into another position, namely the cylinder axis of the second cylindrical surface section. Also this new instantaneous axis of rotation is in a well-defined position relative to the rotary piston. In the next interval of motion, this instantaneous axis of rotation coincides with the cylinder axis of the cylindrical inner wall section, in which now the second cylindrical surface section of the rotary piston is rotatably guided. In this interval of motion, the “first” cylindrical surface section slides along the opposite inner wall section of lager radius of curvature.
In a rotary piston machine of this type, the rotary piston rotates always with the same rotational direction but, alternatingly, about different instantaneous axes of rotation, the axes of rotation “jumping” after each interval of motion. Referenced to the rotary piston, two such instantaneous axes of rotation are defined, namely by the cylinder axes of the diametrically opposite cylindrical surface sections. Referring to the housing and the cavity defined therein, the instantaneous axis of rotation jumps between the “corners” of the oval. Thus, the cylinder axes of the inner wall sections having smaller radii of curvature.
During each interval of motion, the volume of one working chamber increases up to a maximum value, while the volume of the respective other working chamber decreases down to a minimum value. In the ideal case, when the cross section of the rotary piston also is an oval, the volume of the working chamber increases from virtually zero to the maximum value and decreases to virtually zero, respectively. Such a rotary piston machine can be designed as a two stroke or four stroke internal combustion engine or as an engine with external combustion such as a steam engine. It may, however, also be designed to operate as a pneumatic motor, as a hydraulic motor or as a pump.
DE 199 20 289 C1 discloses rotary piston machine, wherein a rotary piston, the cross section of which is an oval of second order, is movable in a cavity, the cross section of which is an oval of third order. For transmitting the movement of the rotary piston, there is a single output shaft extending centrally through the cavity. The output shaft extends through an oval aperture of the rotary piston and carries a pinion. The pinion is in mesh with an internal gear on the inner wall of the aperture.
In the prior art rotary piston machine, the order of the oval defining the cavity is always by one larger than the order of the oval defining the cross section of the rotary piston. A bi-oval rotary piston is guided in a tri-oval cavity. In the blocking positions, the instantaneous axes of rotation of the rotary piston jump relative to the rotary piston between two positions, but jump between at least three positions relative to the housing. The smaller radius section of the rotary piston moves translatorily along the larger radius inner wall section of the cavity. This may cause sealing problems with the sealing between the working chambers. A further problem results from the fact that, in each working cycle, consecutively more than two working chambers is formed, which travel around along the inner wall of the housing.
A similar design is disclosed in applicants' U.S. patent application Ser. No. 10/773,093, filed Aug. 8, 2002 (=WO 03/014527). For ensuring that the kinematics of the instantaneous axis of rotation is unambiguously defined in the blocking positions, one rotational axis is temporarily fixed by mechanical means, in such blocking position.
Luxembourg patent 45,663 to Bleser, filed Mar. 16, 1964 and granted Mar. 30, 1965, describes an internal combustion engine in the form of a rotary piston engine, wherein a housing has an oval cavity and the cross section of the rotary piston is also an oval, wherein, however the order of the oval of the cavity is smaller than the order of the oval of the rotary piston. Thus the cross section of the cavity is an oval of second order, while the cross section of the rotary piston is an oval of third order. Two working chambers are defined between the inner wall of the cavity and the rotary piston. When the rotary piston rotates, the volume of one of the chambers increases, while the volume of the respective other one of the chambers is reduced. The rotary piston rotates always in the same rotary direction but in consecutive intervals of motion from one blocking position to the next blocking position. When the rotary piston has reached one blocking position by rotating about a first axis of rotation, it rotates further to the next blocking position about a second axis of rotation. With this structure, there are two housing-fixed axes of rotation, and the rotary piston, in consecutive intervals of motion, alternatingly rotate about these two axes.
To transmit the rotary motion of the rotary piston, the rotary piston has an aperture therethrough, which forms an oval similar to the contour of the rotary piston. This aperture forms an internal gear.
Two spaced, parallel shafts extend through the aperture. The axes of the shafts coincide with the two axes, about which the rotary piston rotates alternatingly. Pinions are provided on the shafts and mesh with the internal gear of the aperture.